Atrial fibrillation is the most common arrhythmia in the United States. The development of more effective new anti-arrhythmic drugs has been hampered by an incomplete understanding of the molecular mechanisms underlying these arrhythmias. Our research project focuses on studying the molecular mechanisms underlying AF, in particular the role of intracellular calcium-release channel dysfunction. Understanding how calcium channels in the heart are regulated and how new pharmacological compounds may normalize dysfunction of these channels may lead to improved therapeutic strategies for AF. Despite intense focus on understanding the molecular mechanisms that cause AF, and efforts to develop more effective and safer drug therapies to prevent AF, the need for better understanding of AF mechanisms and improved therapy is widely accepted. An emerging line of investigation has been the link between altered calcium (Ca2+) homeostasis and AF-initiation and perpetuation. It is hoped that a better understanding of the role of altered Ca2+ homeostasis in the genesis and maintenance of AF could lead to the development of novel, more effective and safer drug therapies. The applicant proposes to determine the mechanism underlying leaky RyR2 channels in atrial and pulmonary vein myocytes in animal models of AF, and test a novel drug S107 (a rycal), developed in the applicant's laboratory, that binds to RyR2 channels and prevents depletion of calstabin2 from the channel thereby inhibiting pathologic diastolic SR Ca2+ leak. A rycal is now in Phase II clinical studies for heart failure and sudden cardiac death and would be available for testing in AF patients.